In a nation doubly devoted to religion and the antics of celebrities, the Church of Scientology and its movie-star followers have long transfixed Americans.

And now Paul Haggis, the Canadian-born Oscar-winning filmmaker from London, Ont., has become the most famous follower to defect from Scientology, quitting after 35 years to protest the church's apparent opposition to same-sex marriage.

Haggis sent a scathing letter to the church's official spokesman, Tommy Davis, railing against the church's support for Proposition 8, the measure that outlawed same-sex marriage in California. The dispatch went viral on Monday, more than two months after Haggis wrote it, when it
showed up on the blog of a former high-ranking Scientology official who confirmed its authenticity.

Four years after Scientology's biggest poster boy, actor Tom Cruise, piqued America's interest in the religion after several months of loopy public appearances defending Scientology's beliefs, Haggis's letter provides a rare glimpse of the inner workings of an organization that's the subject of suspicion and ridicule.

In the lengthy letter, the 56-year-old Haggis accused Davis of failing to follow through on promises to distance the church from homophobic remarks made by its San Diego branch during the battle over Proposition 8 last year.

"I called and wrote and implored you, as the official spokesman of the church, to condemn their actions," Haggis wrote. "You promised action. Ten months passed. No action."

He added: "The church's refusal to denounce the actions of these bigots, hypocrites and homophobes is cowardly. I can think of no other word. Silence is consent, Tommy. I refuse to consent ... I hereby resign my membership in the Church of Scientology."

The church did not respond publicly on Monday to Haggis's accusations.

In 2006, Haggis became the first screenwriter since 1950 to write two best picture Oscar-winners in consecutive years -
Million Dollar Baby, directed by Clint Eastwood, and
Crash, which Haggis also directed.

Long known for his humanitarian efforts and strong support for civil liberties, Haggis's letter also criticized Scientology for what he called a long-time practice - urging its followers to "disconnect" from anyone in their lives critical of the church.

Haggis accused the church of ordering his wife, who was introduced to Scientology by her parents, to cut off all contact with them due to something "absolutely trivial" they did 25 years ago. He was further angered, he wrote, by Davis's appearance on CNN last year when he denied any such policy existed.

"I was shocked," Haggis wrote. "We all know this policy exists. I didn't have to search for verification - I didn't have to look any further than my own home."

Davis himself is at the centre of scrutiny after removing his microphone and storming off the set during an interview televised Friday on ABC's
Nightline.

The Scientology spokesman was irked when interviewer Martin Bashir asked: "Do you believe that a galactic emperor called Xenu brought his people to earth 75 million years ago and buried them in volcanoes?"

Davis immediately bristled to hear Bashir make reference to part of a Scientology scripture derived from the writings of church founder L. Ron Hubbard. The church has reportedly attempted to keep the Xenu story secret from a non-Scientologist public, fearful it will serve to discredit the religion.

"Okay, Martin, I am not going to discuss the disgusting perversions of Scientology beliefs that can be found commonly on the Internet and be put in the position of talking about things that are so fundamentally offensive to Scientologists that's all," he said.

Bashir persisted, and Davis stormed out.

In his letter, Haggis also chastised Davis and the church for engaging in "smear campaigns" against former executives who have spoken out against Scientology.

"I was truly disturbed to see you provide private details from confessionals to the press in an attempt to embarrass and discredit the executives who spoke out," he wrote. "A priest would go to jail before revealing secrets from the confessional, no matter what the cost to himself or his church."

Haggis added he was "painfully aware" that his own personal information could be used against him.

"Luckily," he wrote, "I have never held myself up to be anyone's role model."

But Marty Rathbun, who left Scientology after 30 years and now serves as a counsellor to those defecting from the church, predicts that Haggis has little to fear.

"They won't dare mess with Paul," Rathbun, who was a critical source in a St. Petersburg Times exposé on Scientology, wrote on his blog on Monday.

"He is far too intelligent, aware, and savvy for them."

Meanwhile, another high-profile Scientologist, John Travolta, has recently provided some positive PR for the church.

For months, it's been rumoured that Travolta was considering leaving the church in the aftermath of the sudden death of his son, Jett, earlier this year. Jett Travolta was profoundly autistic and there have been claims that the church doesn't recognize autism and counselled the Travoltas to avoid treating their son, something Scientology has denied.

But in fact, those close to Travolta told People Magazine, the actor's "faith in Scientology has given him strength to deal with his son's death." He reportedly flies to Clearwater, Fla., where Scientology has a centre, four days a week.